Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $54.49   7.208%   $58.4176   $58.42   $58.40   $58.40  
  Purchase #2 $219.30   10.777%   $242.934   $242.93   $242.95   $242.90  
  Purchase #3 $47.27   5.299%   $49.7748   $49.77   $49.75   $49.80  
  Purchase #4 $208.34   7.614%   $224.203   $224.20   $224.20   $224.20  
  Purchase #5 $194.39   11.853%   $217.431   $217.43   $217.45   $217.40  
  Purchase #6 $222.82   12.772%   $251.2786   $251.28   $251.30   $251.30  
  Purchase #7 $135.26   10.656%   $149.6733   $149.67   $149.65   $149.70  
  7 purchase totals = $1,081.87       $1,193.7123   $1,193.70   $1,193.70   $1,193.70